1. Field of the Invention
The present invention relates to a fluid dynamic-pressure bearing, a spindle motor including the fluid dynamic-pressure bearing and a recording disk driving device including the spindle motor.
2. Background Art
In recent years, spindle motors have been required to have a stable deflection characteristic against vibrations, impacts and the like, since they are required to perform reading and writing from and onto a disk, even in the event that vibrations, impacts and the like are imposed on the spindle motor.
For example, as illustrated in FIG. 6, a thrust dynamic-pressure bearing 4 is formed between the axially upper end surface of a bearing member 1 and the lower surface of a rotor hub 2. A taper sealing portion 6 for preventing the leakage of lubricating fluid to the outside is formed below the thrust dynamic-pressure bearing 4 in the axial direction. The lubricating fluid is retained continuously from the thrust dynamic-pressure bearing 4 to the taper sealing portion 6. A lubricating-fluid flow channel 8 is defined by a flange portion 1a of the bearing member 1 and an annular member 10 mounted to the rotor hub 2 such that it has a substantially L-shaped cross-sectional area. Further, the gaps other tan the bearing gap are defined to have greater dimensions than that of the bearing gap, in order to prevent increases of the torque loss.
However, with the configuration having the thrust dynamic-pressure bearing 4 formed between the upper end surface of the bearing member 1 and the lower surface of the rotor hub 2, a large amount of lubricating fluid is retained in the thrust dynamic-pressure bearing 4 during the rotation of the rotor hub 2, since the thrust dynamic-pressure bearing 4 has a large diameter. Accordingly, if an external force is exerted thereon from outside of the motor, this will cause a large amount of lubricating fluid to move within a short time.
As a result, a large amount of lubricating fluid will move to the taper sealing portion 6 located below the thrust dynamic-pressure bearing 4 in the axial direction, which will make it impossible to retain all the lubricating fluid with the taper sealing portion 6, thereby resulting in leakage of lubricating fluid to the outside of the taper sealing portion 6.
In order to cope therewith, it is possible to increase the gap dimension of the taper sealing portion 6 for enabling the retaining of a larger amount of lubricating fluid. However, there is a limit to the volume of lubricating fluid which can be retained by the taper sealing portion 6.